A stick-shaped ignition coil includes a coil portion and a controller. The coil portion has a cylindrical body case that accommodates a center core, a primary coil and a secondary coil. The controller has a boxy head case that accommodates an igniter. The center core, the primary coil, and the secondary coil form a gap in the body case thereamong. Epoxy resin is filled into the gap through the head case, and the epoxy resin is solidified to be an electrically insulative resin. The gap opens to only the upper side, and extends lengthwise to the lower side. Accordingly, epoxy resin is difficult to be entirely filled throughout the gap.
As shown in FIG. 4, in a conventional ignition coil disclosed in JP-A-10-74652 (U.S. Pat. No. 6,169,471, U.S. Pat. No. 6,094,121, U.S. Pat. No. 6,023,215, and U.S. Pat. No. 6,005,464), a body case 100 accommodates a center core 102, a primary coil 103, and a secondary coil 104. Negative pressure is developed inside the body case 100, so that epoxy resin is filled into the body case 100. Epoxy resin is supplied from a head case 107, and the epoxy resin flows into a gap formed in the body case 100 through a gap between an igniter 108 and the circumferential wall of the body case 100. The epoxy resin is supplied into a resin supplying portion 109 of the head case 107 through a nozzle 110 by a constant volume. When the epoxy resin is excessively supplied into the resin supplying portion 109, excessive epoxy resin overflows around the resin supplying portion 109. Furthermore, the body case 100 is communicated with the head case 107 through a pipe 112, so that air in the body case 100 is vented to the side of the head case 107.
In the conventional structure of the ignition coil, epoxy resin is supplied into the resin supplying portion 109 by the constant amount, so that the epoxy resin is not excessively supplied. However, the resin supplying portion 109 is not effective for enhancing inflow of epoxy resin into the gap in the body case 100.
In addition, an outer core is provided to the outer circumferential side of the primary coil 103 and the secondary coil 104. The outer core is formed in such a manner that a magnetic rectangular plate is bent to be in a C-shape in cross section, so that the outer core is attached to the body case 100. When the outer core is attached to the inner circumferential periphery of the body case 100, resin flows into a gap, which is formed between the inner circumferential periphery of the outer core and the outer circumferential periphery of one of the primary spool and secondary spool, which is on the radially outer side. Thereby, air flows out of the outer core through a pair of slits formed on both radially end sides of the outer circumferential periphery of the outer core, so that epoxy resin and air smoothly flow through the gap in the outer core.
However, when the outer core is attached to the outer circumferential periphery of the body case 100, the gap formed between the inner circumferential periphery of the body case 100 and the outer circumferential periphery of the one of the primary spool and the secondary spool, which is on the outer side, may be circumferentially uniform. Accordingly, inflow of epoxy resin may interfere with outflow of air.
Here, a holder is provided to fix a physical relationship among the center core 102, primary coil 103 and the secondary coil 104. The holder is attached to the directly lower side of the igniter 108, so that the holder covers the center core 102. Thus, the opening of the body case 100 on the upper end side is covered with the igniter 108 and the holder. Accordingly, forming a hole, through which resin flows, becomes difficult.